Field of the Invention
This invention relates to magnetooptical recording elements. More particularly it relates to magnetooptical recording elements having greater reliability, improved resistance to corrosion, improved physical stability under varying temperature conditions, are readily manufactured by simplified techniques and which demonstrate a satisfactory carrier to noise ratio.
In magnetooptic recording devices, rare earth transition metal alloys have been prominently named as suitable materials to achieve a high rotation angle of the planarized laser light, whether the system utilizes the Kerr effect or the Faraday effect. These materials are highly corrosive in air and therefore must be protected by layers disposed adjacent to the rare earth transition metal recording layer.
It has been proposed to utilize in this regard ceramic layers such as, for example, aluminum nitride, silicon nitride, silicon oxides, aluminum oxides, and the like. Such layers are suitable for use in magnetooptical recording elements employing either the Kerr effect or Faraday effect as they are generally transmissive to laser light. However, they suffer the disadvantage that they are difficult to deposit on the surface of the magnetooptic layer in a reliable fashion.
It has also been known to provide a protective layer on the magnetooptic layer by utilizing an active metal that forms a passivating layer including chromium, zirconium, molyldenum, tungsten, tantalum, vanadium, hafnium, titanium, aluminum, magnesium, zinc and the like. Such layers, while they improve the corrosion and oxidation resistance of the magnetooptic layer, suffer from disadvantages including reduction in the carrier to noise ratio because of the transmissivity of the particular material employed and also in that many of these materials interfere with the precise recording of the magnetooptic layer because of the thermal conductivity of the material which spreads out the heat imparted by the recording laser over too broad an area. Thus, each of the two types of corrosion preventive layers suffers because of the inherent disadvantages due to the nature of the material itself.